Nikita Popov bf23b4031e [ValueTracking] Take poison-generating metadata into account (PR59888) ...

In canCreateUndefOrPoison(), take not only poison-generating flags,
but also poison-generating metadata into account. The helpers are
written generically, but I believe the only case that can actually
matter is !range on calls -- !nonnull and !align are only valid on
loads, and those can create undef/poison anyway.

Unfortunately, this negatively impacts logical to bitwise and/or
conversion: For ctpop/ctlz/cttz we always attach !range metadata,
which will now block the transform, because it might introduce
poison. It would be possible to recover this regression by supporting
a ConsiderFlagsAndMetadata=false mode in impliesPoison() and clearing
flags/metadata on visited instructions.

Fixes https://github.com/llvm/llvm-project/issues/59888.

Differential Revision: https://reviews.llvm.org/D142115

2023-01-20 12:18:32 +01:00

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